Industrial Waterproofing and Fluid-Applied Membrane Systems

Article 06 of 24

Evaluating New and Existing Concrete Structures

A waterproofing membrane can only perform when the concrete beneath it is sound, properly prepared, compatible with the selected system, and suitable for accepting a continuously bonded membrane.

Learning Objectives

After completing this article, the reader should be able to:

• Identify important differences between evaluating new and existing concrete.
• Recognize concrete defects that can interfere with membrane adhesion or continuity.
• Classify cracks according to movement, condition, and potential significance.
• Understand the appropriate use of sounding, adhesion testing, moisture testing, and test areas.
• Recognize conditions that require evaluation by a qualified engineer or other specialist.
• Document concrete conditions before surface preparation and membrane installation begin.

Concrete Evaluation Comes Before Surface Preparation

Surface preparation cannot correct every concrete problem. Blasting, grinding, cleaning, patching, and priming may create an acceptable bonding surface, but they do not stabilize a moving crack, replace deteriorated reinforcement, correct structural movement, or stop water pressure originating behind the membrane.

The contractor must first determine whether the concrete is a suitable candidate for the specified waterproofing system. This evaluation should occur before final pricing whenever access and project conditions permit. Conditions that cannot be evaluated during estimating should be clearly identified as exclusions, allowances, or items requiring verification after access is available.

Contractor Evaluation Has a Professional Boundary

A waterproofing contractor evaluates the substrate to determine whether it is ready to receive the specified membrane. That evaluation does not automatically make the contractor responsible for determining the structural capacity or structural safety of the concrete.

When deterioration, movement, cracking, reinforcement corrosion, displacement, deflection, or other conditions suggest a structural concern, the condition should be documented and referred to the project engineer, structural engineer, architect, or other qualified authority. Work should not proceed over questionable concrete without written direction.

Evaluating New Concrete

New concrete should not be assumed ready simply because it looks clean or has reached a particular age. The membrane manufacturer’s written requirements and the project specification determine the required curing, moisture condition, surface profile, strength, cleanliness, and repair procedures.

Information to Review

• Concrete placement dates and curing history.
• Specified concrete strength and available test results.
• Mix design, water-cement ratio, and admixtures when available.
• Curing compounds, sealers, hardeners, densifiers, or bond-breaking materials used.
• Form-release agents used on vertical or formed surfaces.
• Surface finish, texture, and any areas altered after placement.
• Location and type of construction, control, isolation, and expansion joints.
• Tie holes, penetrations, blockouts, drains, terminations, and embedded items.
• Required moisture tests and substrate acceptance criteria.

Conditions to Identify

• Laitance or weak surface paste.
• Bugholes, air voids, honeycombing, fins, ridges, and form offsets.
• Plastic-shrinkage, drying-shrinkage, settlement, or movement cracks.
• Poorly consolidated concrete around penetrations and embedded items.
• Sharp projections capable of damaging the membrane.
• Low areas that may retain water.
• Surface contamination from construction traffic or adjacent trades.
• Incompatible curing compounds, releases, sealers, or treatments.

Do Not Rely on a Generic 28-Day Rule

Twenty-eight days is commonly associated with concrete strength development, but it is not a universal declaration that concrete is ready for every membrane. Concrete age, strength development, internal moisture, surface dryness, ambient conditions, curing method, slab thickness, and membrane chemistry are separate considerations.

Some membrane systems may permit installation earlier under defined conditions. Others impose strict moisture or curing requirements. The contractor should follow the current technical data sheet, written installation instructions, project specification, and documented approval from the membrane manufacturer.

Evaluating Existing Concrete

Existing structures require investigation beyond visible surface appearance. The contractor should determine what the concrete has been exposed to, how it has performed, what repairs have been made, and whether water is entering through cracks, joints, penetrations, adjacent construction, or hydrostatic pressure.

Review the Structure’s History

• Original drawings, specifications, and available repair records.
• Previous waterproofing, coatings, sealers, patches, and joint treatments.
• Known leakage locations and the conditions under which leakage occurs.
• Chemical, wastewater, salt, oil, biological, or process exposure.
• Freeze-thaw exposure, thermal cycling, settlement, or vibration.
• Changes in use, loading, drainage, surrounding grades, or groundwater conditions.
• Previous repairs that failed or cracks that repeatedly reopened.

Conduct a Systematic Visual Survey

Divide the work area into identifiable elevations, rooms, bays, wall sections, or grid locations. Mark observations on drawings or photographs so the same location can be found again after preparation begins.

• Cracks, joints, penetrations, tie holes, and terminations.
• Spalls, scaling, erosion, pop-outs, and exposed aggregate.
• Hollow-sounding or visibly delaminated concrete.
• Exposed reinforcement and rust staining.
• Efflorescence, mineral deposits, dampness, and active water entry.
• Biological growth, oil, grease, chemicals, and embedded contamination.
• Existing coatings, adhesives, mastics, sealers, and unknown materials.
• Irregularities that may prevent uniform membrane thickness or continuity.

Field Observations and Required Actions

Classifying Cracks

A crack should not be treated merely as a groove that needs filling. Its condition and probable movement must be understood before a repair or membrane-detailing method is selected.

Record the Following

• Location, orientation, length, and visible width.
• Whether the crack is dry, damp, leaking, or carrying deposits.
• Whether the crack passes through a wall, slab, joint, penetration, or change in section.
• Whether the two sides are level or displaced.
• Whether previous repairs have reopened.
• Whether the crack appears active, dormant, structural, or nonstructural.
• Whether movement is expected from temperature, shrinkage, settlement, vibration, or loading.

Active cracks and functioning expansion or isolation joints require details capable of accommodating expected movement. A rigid patch or continuously bonded membrane should not be used as a substitute for a properly designed moving-joint detail.

Sounding and Nondestructive Evaluation

Hammer or chain sounding may help identify changes in sound associated with possible delamination or debonded repairs. It is a screening method and should not be represented as a complete structural evaluation.

More advanced nondestructive evaluation may include impact echo, ultrasonic methods, ground-penetrating radar, infrared thermography, half-cell potential testing, and other specialized procedures. Method selection and interpretation should be performed by qualified personnel familiar with the structure and the limitations of the test.

When the survey indicates widespread deterioration or hidden conditions that could affect the repair design, the contractor should request a defined investigation rather than guessing from surface appearance.

Pull-Off Adhesion Testing

Pull-off adhesion testing can help evaluate the tensile strength of the prepared concrete surface, the bond of an existing material, or the performance of a proposed membrane or primer system. ASTM D7234 is specifically intended for pull-off adhesion testing of coatings on concrete using portable pull-off adhesion testers.

The measured value is only part of the result. The failure mode must also be recorded. Failure may occur within the concrete, at the concrete-coating interface, within a coating layer, between coating layers, or in the adhesive used to attach the test fixture.

Test results can be affected by the instrument, fixture geometry, adhesive, scoring method, concrete condition, coating thickness, temperature, and operator procedure. Acceptance values, number of tests, and test locations should be established before testing begins.

Dry-Looking Concrete May Still Contain Moisture

Surface appearance is not a moisture test. Concrete may look dry while moisture moves through the slab or wall, remains within the pore structure, or accumulates under changing temperature and humidity conditions.

Use the moisture-evaluation method required by the project specification and accepted by the membrane manufacturer. Record the test method, equipment, calibration status, test locations, ambient conditions, and results. Moisture testing and water-source investigation will be addressed in greater detail later in this course.

Existing Coatings and Unknown Materials

An existing coating or membrane may appear well bonded while concealing weak concrete, moisture, incompatible repair materials, or localized delamination. The contractor should determine whether the new system is designed and approved for installation over the existing material.

• Identify the existing material when reasonably possible.
• Determine whether hazardous-material testing is required before disturbance.
• Map peeling, blistering, cracking, softening, and loss of adhesion.
• Use adhesion tests to investigate apparently sound areas.
• Confirm chemical compatibility with the proposed primer and membrane.
• Prepare a representative test area before approving the full installation method.

Representative Test Areas and Mockups

A representative test area allows the contractor, owner, specifier, and manufacturer to evaluate the proposed preparation and installation process before full production begins.

The test area should represent actual project conditions and may be used to confirm:

• Removal of existing coatings and contamination.
• The resulting concrete surface profile.
• Concrete repairs and surface leveling.
• Primer absorption, coverage, and compatibility.
• Membrane application and continuity.
• Adhesion-test results and failure modes.
• Appearance of the accepted completed work.

Acceptance of the test area should be documented in writing. The accepted area should remain available as a workmanship reference when practical.

Concrete Acceptance Checklist

Conditions Requiring Further Evaluation

Stop and request direction when the evaluation identifies:

• Exposed, corroded, or visibly damaged reinforcement.
• Widespread delamination, spalling, or loss of concrete section.
• Displaced cracks, recurring cracks, or unusual crack patterns.
• Deflection, settlement, movement, or displaced joints.
• Active water entry or evidence of significant water pressure.
• Concrete that remains weak after the specified preparation.
• Unknown materials that may be hazardous or incompatible.
• Conditions outside the membrane manufacturer’s published limitations.

Documenting Substrate Acceptance

Substrate acceptance should be documented before primer or membrane application conceals the concrete. Documentation protects the owner, contractor, manufacturer, inspector, and design professional by creating a record of observed conditions and agreed corrective work.

A useful acceptance record includes:

• Project, area, elevation, and date.
• Photographs with identifiable locations.
• Crack, joint, repair, and defect maps.
• Preparation methods and equipment used.
• Surface-profile observations or measurements.
• Moisture, adhesion, and other test results.
• Repair materials and installation dates.
• Weather and environmental conditions.
• Unresolved conditions and written disposition.
• Names of parties participating in the acceptance review.

Field Principle: Do Not Coat Over Uncertainty

If the concrete is weak, moving, contaminated, wet beyond the system’s limits, structurally questionable, or not understood, covering it with a membrane does not resolve the condition. It conceals the evidence and may transfer the failure into the new system. Investigate first, obtain written direction, complete the necessary repairs, and verify the substrate before proceeding.

Technical References

• ASTM D5295/D5295M-18: Standard Guide for Preparation of Concrete Surfaces for Adhered Bonded Membrane Waterproofing Systems. ASTM International
• ASTM D7234-22: Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers. ASTM International
• ACI CODE-562-25: Assessment, Repair, and Rehabilitation of Existing Concrete Structures—Code and Commentary. American Concrete Institute
• ICRI Guideline 210.4R-2021: Guide for Nondestructive Evaluation Methods for Condition Assessment, Repair Quality Assurance, and Performance Monitoring of Concrete Structures. International Concrete Repair Institute
• The waterproofing manufacturer’s current technical data sheets, application instructions, approved details, substrate requirements, and written project recommendations.

Professional responsibility: This article provides foundational contractor education and is not a structural assessment, repair design, or project-specific specification. Follow the contract documents, applicable codes, current manufacturer instructions, safety data sheets, and written direction from qualified design professionals. Refer structural concerns to a licensed professional engineer.

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